(i) Field of the Invention
This invention relates to a method and apparatus for cooling electrons, ions or plasma.
(ii) Prior Art
Almost all of the natural objects surrounding us on earth are neutral, and do not occur in a charged state. In order to obtain charged particles such as electrons, ions or plasma, it is necessary to separate the electrons from the nuclei inside atoms, by supplying energy. The energy necessary to ionize say hydrogen gas into electrons and protons is 13.6 eV per atom. To create a plasma consisting of electrons and protons requires supplying this energy by some means. The energy can be supplied either by a static or an alternating electric field. For the static electric field, an anode and cathode configuration is necessary. For an alternating electric field, the energy may be supplied by a radio frequency (RF) oscillator or microwave source. After the gas is ionised, the ions may be extracted by imposing a high voltage on the ionised gas. Normally, in creating a plasma, the gas is disturbed violently, and a very hot plasma is produced. The temperature of the plasma can be characterized by the energy spread .DELTA.E in units of eV (1 electron volt=1.2.times.10.sup.4 Kelvin). For a duoplasma ion source the energy spread is in the range of 15-65 eV. For a microwave generated ion source, the energy spread is of the order of 1 eV. The smallest energy spread is achieved by the Colutron ion source .DELTA.E.perspectiveto.0.2 eV. Such a device is manufactured commercially by Colutron Research Corporation 5420 Arapahoe, Boulder, Colo., 80303, United States of America. Further decrease is limited by the thermal temperature necessary (0.1 eV or 1000 K.) to create the plasma. Hence it is in general very difficult to decrease the energy spread to less than 0.1 eV. Cooling to energy spreads of this order or less may be termed "super-cooling".